1. Field of the Invention
The present invention relates to a driving apparatus, a holding apparatus, an exposure apparatus, and a device fabrication method.
2. Description of the Related Art
An exposure apparatus has conventionally been employed to fabricate a micropatterned semiconductor device, such as a semiconductor memory or a logic circuit using photolithography. The exposure apparatus transfers various types of patterns (circuit patterns) formed on reticles (originals) onto, for example, silicon wafers (substrates).
Along with a recent increase in the degree of integration of semiconductor devices, it is becoming a common practice to transfer patterns finer than ever onto wafers. An exposure apparatus is, therefore, required to have a projection optical system, which is less likely to suffer from wavefront aberration or distortion (i.e., which has an excellent resolving power). To fabricate large-scaled integrated semiconductor devices, it is demanded not only to improve the resolving power of a projection optical system, but also, to improve the overlay accuracy (the accuracy of overlaying several patterns onto a wafer), as an important factor.
To meet this demand, it is necessary to build optical elements, such as lenses, in a projection optical system, while they are precisely positioned (their optical designs are satisfied). It is also necessary to adjust the positions of the optical elements in the projection optical system upon fluctuation (e.g., the influence of an atmospheric pressure variation or heat generated upon exposure) of an exposure apparatus used. In stacking frame bodies that hold the optical elements on each other in the projection optical system, the positions of the frame bodies are adjusted to position the optical elements. This optical element positioning requires close attention to the positional adjustment of the frame bodies, which requires close scrutiny and a great deal of effort.
Under the circumstances, Japanese Patent Laid-Open No. 2005-175271 proposes a driving mechanism (adjusting mechanism), which can easily perform the positioning and position adjustment of an optical element in a projection optical system with high accuracy. Such driving mechanisms are equidistantly arranged at three points on the circumference of an optical element, and can drive the optical element in the vertical direction (Z direction) and inclination directions (θx direction and θy direction) using rectilinear actuators, such as stacked piezoelectric elements. Basically, as shown in FIG. 7, displacement sensors CD for measuring displacements of an optical element OE extend in the Z direction. The position of the optical element OE in three directions (Z direction, θx direction, and θy direction) can be controlled by feeding back the measurement results obtained by the displacement sensors CD to rectilinear actuators DA. FIG. 7 is a block diagram schematically showing the positioning control of an optical element by a conventional driving mechanism.
In recent years, it is also demanded to develop a driving mechanism, which can perform the positioning and position adjustment of an optical element in the Z direction, with a longer stroke and higher accuracy.
Unfortunately, as the stroke of an optical element in the Z direction increases, the conventional driving mechanism inevitably drives it in the θx direction and θy direction in larger amounts. This may excessively incline (tilt) the optical element. As a consequence, the stress of an adhesive bonding the optical element and the cell exceeds a limit. Then, the optical element peels off from the cell (or the optical element is damaged), or plastically deforms as a force produced beyond the stress limit acts on the cell.
The tilt of an optical element can be limited (controlled) using a displacement sensor. However, if the displacement sensor fails, it becomes impossible to limit the tilt of the optical element.